Hydrocracking process

ABSTRACT

Selected nitrogen-containing hydrocarbon fractions are hydrocracked to maximize gasoline production. A fraction is hydrocracked severely in the presence of added hydrogen and a hydrocracking catalyst resistant to organic nitrogen compounds. Naphtha is separated from the resultant product, and the remaining liquid product is then hydrocracked in the presence of a hydrocracking catalyst.

United States Patent Coonradt et al.

3,427,243 2/ 1969 Hass et a1. ..208/1 1 l [72] Inventors: Harry L.coonradtwoodbury; Paul 3,554,899 1/ 1971 Hansford ..208/1 11 Snyder JrPitman both ofN J 3,562,144 2/1971 Child et a1. ..208/11l 3,184,4025/1965 Kozlowski et al...... ..208/59 [73] Assigneez Mobile OilCorporation, New York, 3,304,254 2/1967 Eastwood et al. ..208/1 1 1Primary ExaminerDelbert E. Gantz 2 [2 1 Flled July 1969 AssistantExaminer-G. E. Schmitkons [21] Appl. No.: 840,280 Attorney-Oswald G.Hayes, Andrew L. Gaboriault and Carl D. Farnsworth [52] 0.8. CI...260/1ll, 208/59, 252/455 Z [51] Int. Cl.....Cl0g 13/02, ClOg 37/04,Clb 33/28 [57] ABSTRACT Fled of Search 1 -208/59 l nitrogen containinghydrocarbon fractions [56] References Cited are nydrocracked to maximizegasoline production. A fraction is hydrocracked severely in the presenceof UNITED STATES PATENTS added hydrogen and a hydrocracking catalystresistant to organic nitrogen compounds. Naphtha is separated 3,263,9348/1966 Hansford ..208/1l1 from the resultant product and the remainingliquid ,680 8/1969 Plank et al ..252/455 product is then hydmcracked inthe presence of 3 3,597,349 8/1971 Bertolaclm et al. ..208/1 1 1hydrocracking catalyst 3,620,964 11/1971 Stover et a1 ..208/l113,424,671 1/1969 Kay ..208/59 6 Claims, 1 Drawing Figure Reformer wi 28T) I f 38 /0\ /7 T P 23 Reactor Hessure Pressure Fractionator RGOCTOrSeparator Separator r 3/ .7'4 153/ 38 High 32/ Pressure SeparatorHYDROCRACKING PROCESS Mar. 13, 1973 l I-IYDROCRACKING PROCESS FIELD OFINVENTION BACKGROUND OF THE INVENTION Hydrocracking, includingmulti-stage operation, of hydrocarbon fractions has been known andpracticed for many years. However limitations of hydrocracking catalystshave imposed restrictions upon such operations. For example, nitrogenand/or sulfur contaminants in the feed stocks deactivate and age eventhe most selective hydrocracking catalysts. As a consequence, thefirst-stage hydrocracking operation has been and is now employed as apretreating stage (e.g., desulfurization, denitrogenization, etc.)wherein the contaminants are removed with relatively low conversion offeed stock to naphtha, such that the products contain the contaminantsin amounts tolerable for the second-stage hydrocracking catalyst. Ineffect, the first stage is a feed or charge pretreatment, followed bytrue hydrocracking.

A substantial first-stage conversion of such feed stocks can beaccomplished with a number of hydrocracking catalysts, but withunacceptable or undesirably high catalyst aging rates (as measured by atemperature increase per day for uniform effectiveness) due to suchcontaminants. To compensate, at least in part, reduction in aging ratecan be realized by reducing the feed charge rate (space velocity) or byincreasing hydrogen partial pressure (a function of hydrogenconcentration and total pressure). Each of these compensatorymodifications is unattractive economically.

It has been recognized, therefore, that if substantial conversion couldbe realized in a true hydrocracking first stage, without excessivecatalyst aging, the second stage hydrocracking catalyst and equipmentrequirements could be reduced substantially.

The present invention, therefore, is directed to a method and processfor overcoming the shortcomings of prior practices, and particularly tomaximizing gasoline production in a multi-stage hydrocracking process.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided a process for converting selected gas oils with selectedcatalysts in a multi-stage hydrocracking process. A hydrocarbon fractioncontaining from about 1,000 to about 5,000 parts per million (ppm)organic nitrogen and having a boiling range within the approximatetemperature range of from 400 to 800 F. is contacted, in the presence ofadded hydrogen, with certain hydrocracking catalysts which aresubstantially stable in the presence of organic nitrogen compounds. Suchcontact is with a liquid hourly space velocity of from about 0.5 toabout to provide a conversion per pass to naphtha having an end point ofbelow about 390 of from about to about 70 percent by weight. Theresulting hydrocarbon product is fractionated to recover a naphthaboiling below about 390 F. and a gas oil or heavy naphtha boiling withinthe approximate range of 390 to 750 F. i The gas oil is thenhydrocracked, in the presence of added hydrogen and a hydrocrackingcatalyst under hydrocracking conditions, to convert the gas oilsubstantially completely to a naphtha having an end point below about390 F. and lighter boiling products.

BRIEF DESCRIPTION OF THE DRAWING Illustration of the invention is alsoprovided with reference being made to the accompanying drawing, wherein:

The FIGURE shows a typical flow diagram of a preferred arrangement forpracticing the invention.

Hydrocarbon feed or charge stocks used herein are petroleum fractionshaving an approximate boiling range of from about 400 F. to about 800F., and preferably to about 750 F. Thus, relatively small amounts oflower and higher boiling materials can be present without seriouslyaffecting operation. The charge stocks contain from about 1,000 to about5,000 parts per million (ppm) of organic nitrogen. Such fractionsinclude straight run and catalytically cracked cycle stocks of light gasoil character, and mixtures thereof, particularly those derived fromCalifornian crudes.

The process is particularly desirable for converting highly aromaticcatalytic cycle stocks which themselves are relatively poor chargecomponents for recycle in catalytic cracking. For example, the total ofthe aromatic and olefin content of such stocks can range from stocks orblends thereof can also be used, including straight run and coker gasoils and the like, and blends thereof.

The aforesaid petroleum fractions can contain sulfur in amounts of up toabout 5 percent by weight, since sulfur content up to this level is notcritical in the process.

Charge stocks of the boiling range employed have inconsequential metalcontent. However, if the metal content of the charge should beabnormally high for some accidental occurrence in refinery operation, asmall quantity of a catalyst other than the first-stage hydrocrackingcatalyst can be employed in advance of the latter catalyst. Suitablecatalysts for this purpose include those with Group VIB-VIIIhydrogenation components (e.g., cobalt molybdena) on amorphous supportssuch as alumina or alumina-silica.

HYDROCRACKING CATALYSTS The catalyst in the first hydrocracking stage isof a critical nature, whereas the catalyst in the second hydrocrackingstage can be any one of a number of F IRST-STAGE CATALYSTS The catalystis comprised of both an amorphous acidic component and an acidiccrystalline aluminosilicate in weight ratios of from about 20 to about80 and from about 80 to about 20, respectively.

The amorphous component has an activity index (A1) of 25 or greater.Typical examples comprise representative catalytic cracking catalystssuch as silica-alumina, silica-zirconia, silica-magnesia,silica-alumina-thoria, silica-alumina-fluoride, silica-zirconiaclay,acid treated montmorillonite clay and the like. A preferred component issilica-alumina.

The crystalline aluminosilicates have ordered internal structures withpore sizes available between 6 and 15 angstrom units. Examples of suchzeolites are X, Y, L, ZSM-4, ZSM-5, mordenite and the like. A low alkalimetal content is required; the sodium content of such zeolites should beless than about 2 percent by weight and preferably less than about 1percent by weight. The sodium can be removed and replaced by any wellknown means such as ion-exchange. An example is given in U.S. Pat. No.3,210,267. Suitable cations include the rare earths, calcium, magnesium,manganese, and ammonium (convertible to hydrogen ion on calcination).The rare earths are particularly preferred.

The crystalline aluminosilicates can be prepared by conventionalmethods. Another mode of preparing such material is by solid-solidexchange of clay with a sodium zeolite (e.g., sodium Y with clay asdescribed in U.S. Pat. No. 3,391,088). Still another method is theconversion of clay with alkaline materials as described in U.S. Pat. No.3,431,218. In these cases, the sodium limit of 2 percent by weight withless than 1 percent by weight preferred, refers to the exchangeablesodium of the crystalline components of the product.

The catalysts also include hydrogenation components which comprise anyof the well-known hydrogenation components such as Group V1 B-group Vlllcombinations, tungsten, molybdenum, and noble metals. Preferred arecombinations of nickel-tungsten, cobalt-tungsten, nickel-molybdenum, andcobaltmolybdenum, with nickel-tungsten being illustrated in thefollowing representative examples. Weight percent of nickel can varyfrom about 1 to about 10, with 2-7 preferred; weight percent of tungstencan vary from about 3 to about 30, with 5-20 preferred. Similar atomicratios of 1:2 to 2:1 apply with cobalt and molybdenum. The hydrogenationcomponents need not be the same on the amorphous and crystallinecomponents of the catalysts.

These catalysts can be prepared by conventional methods. Particularlyeffective methods for catalysts of the preferred types are described inU.S. Pat. Nos. 3,173,854 and 3,304,254, and U.S. Pat. application Ser.No. 743,334, filed July 9, 1968.

The pertinent descriptions given of the catalysts in the aforesaidpatents and patent application are incorporated herein by reference.

SECOND-STAGE CATALYSTS The first stage effectively upgrades the productboiling above naphtha such that a wide variety of conventionalhydrocracking catalysts can be used in the second stage. These includeamorphous, crystalline aluminosilicates and mixed acidic components.Hydrogenation components include noble metals, nickel, Group Vl B-Vlllcombinations, and the like.

The quantities of the effective hydrogenation components are the same asdescribed in connection with the first-stage catalysts. Noble metalhydrogenation components are generally used in amounts of about 0.5-4percent by weight. Examples include platinumsilica-zirconia,nickel-silica-alumina, nickel-tungstensilica-zirconia-clay, palladiumacid Y, platinum REX- alumina, etc. A mixed base catalyst such as thetype described in Example 1A following is particularly effective.

HYDROCRACKXNG As indicated above, the selected hydrocarbon fraction orfractions are cracked in contact with the aforementioned catalysts inthe presence of added hydrogen in a plurality of stages. ln the initialhydrocracking, operating conditions and particularly temperature are soselected as to provide for substantial conversion per pass to a naphthaproduct having an end point below about 390 F., of from about 20 toabout percent by weight, at relatively high space velocity and with lowcatalyst aging rates. In a second hydrocracking stage, the productboiling about about 390 F. is converted substantially completely to anaphtha product with an end point below about 390 F. and to lighterboiling products.

Operating conditions for the first-stage hydrocracking operation areprovided below:

Broad Preferred Temperature, F. 675-875 725-825 Pressure, psig 1500-50002000-3000 LHSV, v/v/hr. 0.5-5 1.5-3 Gas recycle, H

equivalent, 3500-30000 4000-10000 scf/b Conversion, wt. 20-70 30-60.

Operating conditions are selected with the catalyst and charge stock soas to realize desirably low catalyst aging rates, of about 01 F. or lessper day. Thus, the operating conditions recited above are modified inrelation to the catalyst and/or charge employed. For example, increasein the nitrogen and condensed polycyclic aromatic content of the chargerequires more severe operating conditions within the ranges soexpressed, in order to maintain catalyst aging rates of less than about0. 1 F. per day. Further, there is a relationship between the operatingconditions, as between hydrogen partial pressure (a function of pressureand gas recycle rate) and space velocity; an increase in hydrogenpartial pressure makes possible an increase in permissable spacevelocity.

Operating conditions for the second-stage hydrocracking are not criticaland can be varied widely, as indicated by the following conventionalhydrocracking conditions:

Temperature, F. 500-900 600-850 The most desirable charge for thesecond-stage hydrocracking operation is the first-stage product boilingabove about 350400 F., however, lower initial boiling points areacceptable. The end point of the second-stage charge need not be thesame as that of the first-stage product.

HYDROGEN Pure hydrogen can be used. However, hydrogen of low purity,obtained by recycle or other hydrogenating process can be used, but itis recommended that the REFORMING The naphtha formed by the multi-stagehydrocracking operation can be reformed under customary reformingconditions. Suitable catalysts are platinum group metals with or withouta halogen, particularly chlorine. Reforming conditions are typified byand include:

Temperature, "F. 900-980 Pressure, psig 500-1500 LHSV 0.5-3.

ILLUSTRATIVE EXAMPLES The following examples illustrate, and in no senselimit the invention.

EXAMPLE 1 l.-A. A catalyst of the mixed crystallinealuminosilicate-amorphous type required was prepared in the followingmanner.

An equal weight mixture of rare earth aluminosilicate X (containingapproximately 28 weight percent of rare earth oxides and 0.8 weightpercent of sodium), and silica-alumina (containing approximately weightpercent of alumina) is impregnated with a slurry of nickel nitrate andammonium tungstate, and is extruded after adjusting to extrudableconsistency with water and adding polyvinyl alcohol as an extrusion aid.The extrudate is dried at 250 F. and is calcined 3 hours at l,000 F.

The catalyst has the following properties:

Surface area, square meters per gram 327 Partial density, g/cc 1.25 Realdensity. g/cc 3.26 Packed density, g/cc .7738 Pore volume, cc/g .495Pore diameter, A 60 Crushing strength, lbs/inch 7O Composition, wt

Nickel 4.26 Tungsten 10.5 Sodium 044 Silica 51.6 Rare earth oxides 11.6Alumina 17.6

l.-B. A crystalline aluminosilicate in the following manner. I p

A calcined rare earth aluminosilicate X is treated with a solution of 10percent ammonium chloride, washed, dried, pelleted, and calcined 3 hoursat 1,000 F. It is then vacuum impregnated with a chloropla tinicacid-sodium hydroxide solution containing 0.256 g sodium per gram ofplatinum, heated in a covered vessel 16 hours at 230 F., treated withnitrogen to 450 F. and reduced with hydrogen. The finished catalyst has3.1 weight percent platinum and a surface area of 422 square meters pergram.

catalyst is prepared EXAMPLE 2 Charge stocks used in these studies arecatalytic cycle stocks prepared in a commercial catalytic cracking unit.The have the following properties:

2-A 2-B 2-C Gravity, AP1 17.2 17.5 19.8 Nitrogen, ppm 2400 2400 700Hydrogen, wt. 10.13 10.12 10.62 Sulfur, wt. 1.00 0.94 2.04 Aniline No.,F. 62.1 59.7 Distillation D86 IR? 443 437 482 5% 474 470 631 10% 493 484643 30% 520 517 667 50% 551 550 686 593 589 701 90% 648 649 728 E.P. 693680 752 Recovered 99.0 99.0 98.0 Aromatics plus Olefins, vol. 65.4

EXAMPLE 3 A first stage operation is conducted with a crystallinealuminosilicate catalyst (3.1 weight percent platinum on REX). As shownin Examples 3F and 36 of the tabulated data below, there is marked agingequivalent to about 1 F./day loss in activity.

With the mixed base catalysts, however, excellent yields of high qualityproducts are obtained as shown in Examples 3A through 3E.

With the mixed base catalysts at an average conversion of about 20weight percent, the aging rate is approximately 5 005 F./day.

With the mixed base catalyst at an average conversion of about 41 weightpercent, the aging rate is approximately 5 003 F./day.

Pt Rex I Mixed base lilaterial-balance sample 3A 3B 3C 31) 3E Catalyst"l A l-A l-A 1-A l-A Cl|urge 2-15 2-13 2-A 2-A 2-A lressure, p.s.i.g.. 2,0 2, 240 2, 240 2, 240 2, 240 Liquid hourly space vcloe 1. 7 1. 7 1.7 1.7 1. 7 'lemp., 1*., avg. catalyst 737.13 737. 7 737. X 768. 7 768. 3Hydrogen, s.c.i./hbl 7, 520 7, 685 7, 415 7, 215 7, 400 Hydrogenc0nsump., s.c.l'./h 1,606 1,506 1,550 1,8115 1,947 Methane, wt. percent.11 .08 .07 .14 .18 Ethane, wt. percent. .14 .14 .14 26 .40 Propane, wt.percent. 46 .46 .38 .80 1.00 Isobutane, vol. percent- 0.7 0. 7 0. B 1. 92. 1 Normal butane, v01. percent 0.9 0.8 O. 9 1. 7 2. 1 C5-C6, v01.percent. 3. 7 3. 4 3. 6 8.0 10. 6 Heavy naphtha, vol. percent 21.0 20. 720. 9 36. 8 36. 7 Higher boiling pr0d., vol. percent- 84. 1 83.7 83. 766.3 64. 0 Product inspection:

Cs grav1y,, API 71. 3 73. 2 70. 4 08.9 67.8 Cu octane, R+3 96. 2 95. 7

vy. naBhtgram, API 40 8 40.4 40. 4 44. 4 44. 5

Octane, R+3 90.1 90. 6 00. 2

Paraflins, vol. percent- 9.6 9. 5 9. 8

Naphthenes, vol. percont 55. 3 54. 2 55.0

Aromatics, vol. percent. 35. 0 36. 3 36. 3 Higher boiling product:

' Gravity, API 26. 8 2G. 7 24. 6 29. 7 29. 8

Dist. D86:

IBP 446 458 Parafllns, vol. percent 13. 0 Naphthenes, vol. percent 41. 1

Aromatics, vol. percent 45.9

Nitrogen, p.p.m

Sulfur, p.p.n1 60 Aniline N0., F. 102. 0 101. 5

Weight percent conv .0--

Aging rate, F./day.

EXAMPLE 4 With reference to the FIGURE, a charge of 100 barrels of ahydrocarbon fraction having a boiling range of 440-700 F consisting of100 percent of cycle stock from Fluid Catalytic Cracking and containingabout 2,400 ppm of organic nitrogen and about 1 percent by weight ofsulfur, is passed from line 10 to hydrocracking unit 11. Hydrogen inline 12, approximately 2,000 SCF/B required for reaction and losses, ismixed with the hydrocarbon fraction in line 10 and is so passed intounit 11. Unit 11 is operated at 2,900 psig inlet pressure and a LHSV of1.7. A temperature of about 775 F. is required initially; this is raisedperiodically to compensate for a relatively small catalyst activity losswith time. The catalyst in unit 11 is the catalyst of EXAMPLE l- A.

The product formed in unit 11 is removed via line 13 to an intermediatesection of high pressure separator 14, which is operated at about 2,800psig. Water in line 15 is injected into the product in line 13, in orderto remove inorganic products such as ammonium hydrogen sulfide, ammoniumsulfide and the like from separator 14 through line 16. Hydrogen in theproduct is removed overhead through line 17 for recycle to lines 12 and10, and thence to unit 11, and for recycle directly as a quench to unit11 via line 18. The gas in line 17 is so recycled to unit ll to providea net hydrogen rate of about 5,500 SCF/B ofcharge.

The substantially hydrogen-free product in separator 14 is passedthrough line 19, and is reduced in pressure to about 300 psi through areducing valve (not shown) in line 19. The product is then passed to anintermediate section of low pressure separator 20. Gaseous products areremoved from separator 20 through overhead line 21. The productremaining in separator 20 is passed through line 22 to an intermediatesection of stabilizer 23, for removal of light hydrocarbons ranging frommethane to isopentane as an overhead gaseous fraction via line 24.

The stabilized product in stabilizer 23 is comprised of approximately Chydrocarbons. it is passed through line 25 to an intermediate section offractionator 26. A light naphtha boiling approximately from isopentaneto 180 F. end point is removed as an overhead product through line 27. Aheavier naphtha with an ASTM boiling range of approximately 225390 F. isremoved from fractionator 26 through line 28. A bottoms product isremoved from fractionator 26 through line 29 and is passed to a secondhydrocracking unit 30.

in the first stage operation, there are obtained from 100 barrels ofcharge:

4.0 barrels butanes 10.3 barrels light naphtha 36.6 barrels heavynaphtha 64.6 barrels higher boiling l-l5.5 barrels Total This representsa conversion of about 35.4 percent by volume to products boiling belowabout 390 F.

Added to the higher boiling fraction in line 29 is hydrogen from line31. Hydrogen used for reaction and make up totals about 1,700 SCF/B. Therecycle gas rate in line 31 is about 4,400 SCF/B. The catalyst in unitis the same as that in unit 11. Unit 30 is operated at approximately 1.5LHSV with about percent conversion per pass to products boiling belowabout 390 F. Inlet pressure is about 1,510 psig with a temperature ofabout 625 F.

The entire reaction product from unit 30 is removed from unit 30 throughline 32 to high pressure separator 33. Hydrogen is separated from theproduct in separator 33 and is recycled through line 31 to line 29 andhydrocracking unit 30, and, in part directly as a quench to unit 30through line 34. Hydrocarbon product in separator 33 is passed throughline 36 and is mixed with first-stage liquid product in line 19 forpassage to separator 20, stabilizer 23 and fractionator 26.

In the two stages, there are obtained from each 100 barrels of charge:

350 lbs hydrogen sulfide equivalent 95 lbs ammonia equivalent 50 lbsmethane I20 lbs ethane 590 lbs propane.

Other products are:

barrels of isobutane barrels of normal butane barrels of light naphthabarrels of heavy naphtha barrels Total The light naphtha in line 27 hasan API gravity of 82.6 and an octane number (research with 3 ml TEL) of98.8

The heavy naphtha in line 28 has an API gravity of 44.9. It has anoctane number (research method with 3 ml TEL) of 85.9 and is comprisedvolumetrically of 21 percent paraffins, 57 percent naphthenes and 22percent aromatics. It is thus an excellent reformer charge.

The heavy naphtha in line 28 is passed to reformer 37, as is hydrogen inline 38, and is reformed at 550 psig over a platinum-alumina catalyst ata hydrogen to hydrocarbon recycle ration of 12/1 at 1 space velocity togive a Cfireformate of l02-octane number (research method plus 3 ml ofTEL). The resulting reformate product is removed from reformer 37through line 39, and is sent to conventional separating andfractionating units (not shown).

The combined hydrocracking-reforming yields are as follows (per 100barrels of original charge):

Hydrogen consumption 2200 SCF/B 350 lbs hydrogen sulfide equivalent 395lbs ammonia equivalent 295 lbs methane 5l5 lbs ethane 1240 lbs propanel0.2 barrels of isobutane 6.6 barrels of normal butane 27.8 barrels oflight naphtha 76.2 barrels of C reformate 20.

l 8 barrels Total only the second-stage naphtha can be used without Ireforming reformed. The charge for reforming generally will comprisenaphtha boiling from about C, I

hydrocarbons to 390 F. ASTM end point and such a charge can also besplit into multiple fractions for reforming.

As a modification of the processing system shown in the FlGURE, theproduct in line 29 can be charged to a fractionator (not shown) in orderto maximize and remove jet fuel therefrom and the balance of the productfrom line 29 can then be charged to hydrocracking unit 30. Alternately,using similar fractionation, but for higher quality jet fuel, theproduct from separator 14 removed through line 19 can be charged, withor without removal of lighter components, to hydrocracking unit 30.

The rare earth mixtures of Examples lAa'nd 18 consist principally ofcerium, lanthanum, praseodymium and neodymium, together with smalleramounts of other rare earths.

What is claimed is:

l. A method for converting a hydrocarbon charge of low API gravityboiling below about 800 F. having combined organic nitrogen compounds inamounts ranging from about 1,000 to 5,000 ppm t 9 form naphtha boilingrange product which comprises contacting said nitrogen-containinghydrocarboncharge with a mixed base hydrocracking catalyst comprising anacidic crystalline aluminosilicate cracking com ponent containingsubstantial amounts of rare earth oxides in combination with an acidicamorphous cracking component having an activity index of about 25 orgreater in a weight ratio of from about 20 to 80 parts of one crackingcomponent to the other, said cracking base provided with non-noble metalhydrogenationdehydrogenation activity selected from the hydrogenationcomponents of Group W8 and Group VIII and effecting said conversion ofsaid hydrocarbon'charge with said hydrocracking catalyst underhydrocracking conditions selected to produce naphtha boiling rangeproduct at a conversion level restricted to within the range of 20 toabout percent by weight whereby the aging rate of the catalyst ismaintained not to exceed about 0. 1 F. per day.

2. The method of claim 1 wherein the conversion per pass to naphthaboiling product is restricted to within the range of about 30 to about50 percent by weight.

3. The method of claim 1 wherein the catalyst comprises a rare earthexchanged X-type zeolite and a silica-alumina matrix.

4. The method of claim 1 wherein the hydrogenation-dehydrogenationcomponent comprises nickel or b It dm 1 bde m tun sten. 5. Tl'l met% dof lilain i 1 wh erein the hydrogenation component is a mixture ofnickel and tungsten and the total catalyst composition contains betweenabout l and about 20 weight percent of nickel and between about 5 and 40weight percent of tungsten.

6. The method of claim 1 wherein said naphtha product is subjected tocatalytic desulfurization prior to catalytic reforming.

1. A method for converting a hydrocarbon charge of low API gravityboiling below about 800* F. having combined organic nitrogen compoundsin amounts ranging from about 1,000 to 5,000 ppm to form naphtha boilingrange product which comprises contacting said nitrogen-containinghydrocarbon charge with a mixed base hydrocracking catalyst comprisingan acidic crystalline aluminosilicate cracking component containingsubstantial amounts of rare earth oxides in combination with an acidicamorphous cracking component having an activity index of about 25 orgreater in a weight ratio of from about 20 to 80 parts of one crackingcomponent to the other, said cracking base provided with non-noble metalhydrogenation-dehydrogenation activity selected from the hydrogenationcomponents of Group VIB and Group VIII and effecting said conversion ofsaid hydrocarbon charge with said hydrocracking catalyst underhydrocracking conditions selected to produce naphtha boiling rangeproduct at a conversion level restricted to within the range of 20 toabout 70 percent by weight whereby the aging rate of the caTalyst ismaintained not to exceed about 0.1* F. per day.
 2. The method of claim 1wherein the conversion per pass to naphtha boiling product is restrictedto within the range of about 30 to about 50 percent by weight.
 3. Themethod of claim 1 wherein the catalyst comprises a rare earth exchangedX-type zeolite and a silica-alumina matrix.
 4. The method of claim 1wherein the hydrogenation-dehydrogenation component comprises nickel orcobalt and molybdenum or tungsten.
 5. The method of claim 1 wherein thehydrogenation component is a mixture of nickel and tungsten and thetotal catalyst composition contains between about 1 and about 20 weightpercent of nickel and between about 5 and 40 weight percent of tungsten.